Anisotropic thermal conduit

ABSTRACT

An anisotropic thermal conduit having an outer cylindrical tube; and an anisotropic thermal material disposed with the outer cylindrical tube.

CROSS REFERENCE TO RELATED APPLICATION

This is a Continuation Application of application Ser. No. 14/879,647,filed Oct. 9, 2015, which application is hereby incorporated herein byreference in its entirety.

TECHNICAL FIELD

This disclosure relates generally to thermal conduits and moreparticularly to anisotropic thermal conduits.

BACKGROUND

As is known in the art, thermal conduits are used in many applications.One application is in heat spreaders, sometimes also referred to as heattransfer interfaces in extracting heat from a heat source andtransporting the exported heat to a heat sink. Further, in order to makea robust, high reliability head spreader, the coefficient of thermalexpansion (CTE) between the heat spreader and the heat source should beclosely matched and the CTE between the thermal spreader and the heatsink should be closely matched. In electrical applications, for example,these additional interfaces can result in degraded thermal performanceand increased electrical parasitics thereby increasing electrical loss,reducing efficiency and/or adding cost and complexity to the systemdesign.

Current method for heat spreader design has been to add intermediateheat spreader transitions between low CTE and typically poorer thermalconductivity materials to high thermally conductive and typically highthermal expansion materials such as copper as the CTE mismatch interfacebetween the high conductivity metals and the low thermally conductivematerial semiconductor is, in many applications, too great to reliablymake a direct transition. This approach adds design complexity, cost,and performance loss due to the additional thermal and electricalinterfaces.

As is known in the art, Thermal Pyrolytic Graphite (TPG) materialexhibits very anisotropic thermal conductivity such that, within thebasal plane, the thermal conductivity can be ˜1600 W/m-° K (4× ofcopper) and perpendicular to the basal plane is ˜10 W/m-° K ( 1/40 ofcopper). More particularly, graphites possess anisotropic structures andthus exhibit or possess many properties that are highly directional e.g.thermal and electrical conductivity and fluid diffusion. Still moreparticularly, graphites are made up of layer planes of hexagonal arraysor networks of carbon atoms. These layer planes of hexagonally arrangedcarbon atoms are substantially flat and are oriented or ordered so as tobe substantially parallel and equidistant to one another. Thesubstantially flat, parallel equidistant sheets or layers of carbonatoms, usually referred to as graphene layers or basal planes, arelinked or bonded together and groups thereof are arranged incrystallites. A sheet of pyrolytic graphite may be described as havingthree directional axes; an a-axis and a b-axis which are parallel to thesurface of deposition of the basal planes and perpendicular to eachother, and a c-axis of which is perpendicular to both the a-axis and theb-axis and to the basal planes. The thermal properties of pyrolyticgraphite are strongly affected by its structural anisotropy. Pyrolyticgraphite acts as an excellent heat insulator in the c-axis direction(which is along the direction of deposition of the graphite;perpendicular to the plane of the surface upon which the graphite isbeing deposited) and as a relatively good heat conductor in the planescontaining the a-axis and the b-axes.

It should be understood that the term “thermal pyrolytic graphite”(“TPG”) may be used interchangeably with “highly oriented pyrolyticgraphite” (“HOPG”), or compression annealed pyrolytic graphite (“CAPG”).

It is also known in the art that TPG materials have been used asanisotropic thermal conduits in planar heat spreaders as shown in FIG.1; the basal plane being represented by dotted lines.

SUMMARY

In accordance with the present disclosure, a thermal conduit is providedcomprising: an outer cylindrical tube; and an anisotropic thermalmaterial disposed with the outer cylindrical tube.

In one embodiment, the anisotropic thermal material is pyrolyticgraphite (TPG).

In one embodiment, the anisotropic thermal material has a greaterthermal conductivity along a longitudinal central axis of the tube thanthe thermal conductivity of the anisotropic thermal material along adirection perpendicular to the longitudinal axis of the tube.

In one embodiment, the anisotropic thermal material has a smallerthermal conductivity along a longitudinal axis of the tube than thethermal conductivity of the anisotropic thermal material along adirection perpendicular to the longitudinal axis of the tube.

In one embodiment, the thermal conductivity of the anisotropic thermalmaterial has conducts heat radially outwardly from the longitudinal axisof the tube.

In one embodiment, the anisotropic thermal material has a basal planeperpendicular to the longitudinal axis of the tube.

In one embodiment, the anisotropic thermal material has a basal planeparallel of the longitudinal axis of the tube.

In one embodiment, the anisotropic thermal material has a basal planeperpendicular extending radially outwardly from the longitudinal axis ofthe tube.

In one embodiment, the anisotropic thermal material has a smallerthermal conductivity along a direction circumferentially within the tubethan the thermal conductivity of the anisotropic thermal material alonga direction along the longitudinal axis of the tube.

In one embodiment the anisotropic thermal material is embedded with thetube.

In one embodiment the tube is a thermally conductive metal.

In one embodiment, an inner tube or rod is included and the anisotropicthermal material is disposed between the inner tube or rod and the outertube.

In one embodiment the outer tube has a circular cross-section.

In one embodiment the inner rod or tube has a circular cross-section.

In one embodiment, the outer tube may be a metal, a ceramic, or aplastic

In one embodiment, the outer tube may be MoCu, WCu, W, Mo, Cu, forexample.

In one embodiment, the thermal conduit is bendable.

With such a heat conduit, embedding the anisotropic thermal materialinside metal tube walls simultaneously achieves both high and lowthermal conductivities in a desired configuration. Such a heat conduitprovides intimate transitions from a heat source to a heat sink. Lowthermal expansion materials can be used as external mating materialwhile the anisotropic thermal material allows for high thermalconduction in two directions. This tubular structure allows for newpackaging concepts that direct the heat and for opportunities forintegrating liquid cooling while maintaining a low CTE metal externallyeliminating transitions within a within a cooling system or subsystemincluding microelectronic packaging due to CTE management.

Further, with such anisotropic thermal conduit, because TPG has adensity of 2.25 g/cm³, which is ¼ of copper's weight the heat spreaderincorporating TPG can also significantly reduce the weight of the heatspreader. The TPG provides the directional thermal conductivity andinner tube or rod and the outer tube provide protection and mechanicalstrength to the heat spreader. The inner tube can additionally be usedas part of fluid cooled system.

The details of one or more embodiments of the disclosure are set forthin the accompanying drawings and the description below. Other features,objects, and advantages of the disclosure will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an anisotropic thermal material heatspreader according to the PRIOR ART;

FIG. 2A-2D are a series of sketches showing a method for fabrication ananisotropic thermal conduit according to the disclosure at various stepsin the fabricating thereof; FIG. 2D showing a perspective view of thecompleted anisotropic thermal conduit in accordance with the disclosure;

FIGS. 3A-3F are a series of sketches showing a method for fabrication ananisotropic thermal member used in the anisotropic thermal conduit ofFIG. 2D in accordance with an alternative embodiment of the disclosure;

FIGS. 4A and 4B show an exemplary pair of applications for theanisotropic thermal conduit shown in FIG. 2D; FIG. 4A showing theconduits between a heat source and a heat sink with their longitudinalaxis perpendicular to the surfaces of the heat source and the heat sink;and FIG. 4B showing the conduits between the heat source and the heatsink with their longitudinal axis parallel to the surfaces of the heatsource and the heat sink;

FIGS. 5A-5F are a series of sketches showing a method for fabrication ananisotropic thermal conduit in accordance with the disclosure; FIGS.5B-5E being end views of the conduit; and FIG. 5F showing a perspectiveview of the completed anisotropic thermal conduit in accordance with thedisclosure;

FIGS. 6A-6I are a series of sketches showing a method for fabrication ananisotropic thermal conduit in accordance with another alternativeembodiment of the disclosure; FIGS. 6D-6H being end views; and FIG. 6Ishowing a perspective view of the completed anisotropic thermal conduitin accordance with the disclosure; and

FIGS. 7A-7D are a series of sketches showing a method for fabrication ananisotropic thermal conduit in accordance with the disclosure; FIGS.7A-7C being end views of the conduit; and FIG. 7D showing a perspectiveview of the completed anisotropic thermal conduit in accordance with thedisclosure; and

FIG. 8 is an end view of a thermally conductive conduit that was used ina model to calculate thermal conductivity of the embodiments shown inFIGS. 2D, 5F, 6I, and 7D.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Referring now to FIGS. 2A-2D, an outer cylindrical tube 10, here forexample, MoCu, WCu, W, Mo, Cu, is provide, as shown. It is noted thatthe tube 10 is elongated along a central, longitudinal, here Z axis, asshown; it being understood that the tube 10 may have a length greaterthan, equal to, or less than its diameter.

Next, the tube 10 is cut along the Z axis into two halves 10 a, 10 b,each having a semi-circular cross section, as shown in FIG. 2B.

Next, the inner surface of 11 a, 11 b of each half 10 a, 10 b,respectively, of the tube 10 are coated with a reactive metal brazealloy 12 a, 12 b, respectively, as shown in FIG. 2C, here for exampleusing a reactive metal braze alloy such as Indium-Copper-Silver in aconventional brazing or a vacuum brazing process. A reactive metal suchas titanium or vanadium may be used as a braze filler or deposited onthe surfaces to be brazed.

Next, anisotropic thermal materials, here TPG members 14 a, 14 b areplaced on the reactive metal braze alloy 12 a, 12 b, respectively, asshown in FIG. 2C. It is noted that in one configuration the basal planes(represented by dotted lines 15) are parallel to the longitudinal axisZ.

More particularly, FIG. 3A-3F show steps used to form the TPG members 14a, 14 b. Thus, referring to FIG. 3A, a block 17 of thermal anisotropicmaterial, here for example, TPG, it being understood that other thermalanisotropic materials may be used, is formed using for example, anyconventional deposition process. The basal planes 15, having both thea-axis and b-axis of the TPG block 17, are formed perpendicular to thedirection of the deposition (along the c-axis of the TPG block 17); thedirection of the deposition being indicated by arrows in FIG. 3A. Asnoted above, the basal planes are represented by the dotted lines 15.

Next, the block 17 is cut along a cutting plane CP a-axis and the c-axisof the TPG material 17 as indicted in FIG. 3B thereby separating theblock 17 into two sections 19 a, 19 b; an exemplary one of the sections19 a, 19 b, here section 19 a, being shown in FIG. 3C and is positionedwith the basal planes 15 orientated as shown. Next, the section 19 a iscut along a curved cutting surface CS1 into a TGP member 21 as shown inFIGS. 3C and 3D to form a TPG member 21 shown in FIG. 3D having across-section shaped to fit within the inner surface 13 a, 13 b (FIG.2B) of a corresponding one of the sections 10 a, 10 b with the coatedreactive metal braze alloy on tube 10. Thus, here with the tube 10 (FIG.2A), TPG member 14 a, 14 b (FIG. 2C) has a circular cross section in thec-axis, b-axis plane and the TPG member 21 extends along the a-axis asshown the in FIGS. 3C and 3D. Thus, the a-axis and the b-axis of the TPGmaterial (the basal plane 15) is in the spatial X-Y plane shown in FIGS.3C and 3D. It should be understood that the inner surface 11 a, 11 b(FIG. 2B) of the tube 10 is here shown having a circular cross section,the tube 10 may have an oval cross section, a square cross section,rectangular cross section, or any regular or irregular polygon crosssection or a cross section along any preferably, continuous closed loopin which case the member 21 would be cut along the closed loop.

Next, an inner region of the member 21 is cut along a curved surface CS2to form the TPG member 14 b (FIG. 2C) having a semi-circular hole 25through the center of member 21 along a direction parallel to thea-axis, as shown in FIG. 3F. It should be understood that the secondsection 19 b of TPG (FIG. 3B) is processed as described for TPG section14 b producing the pair of shaped TGP members 14 a, 14 b (FIG. 2C).

Next, and referring again to FIG. 2C, a reactive metal braze alloy 16 a,16 b is applied to the exposed surface of each one of the shaped memberTGP members 14 a, 14 b, respectively, as shown, as shown in FIG. 2C toprovide an upper structure 29 a and a lower structure 29 b, as shown inFIG. 2C.

The bottom surface 30 a of the upper structure 29 a, and/or the uppersurface 30 b of the lower structure 29 b, here for example only thebottom surface 30 a of the upper structure 29 a is coated with areactive metal braze alloy 32, such as Indium-Copper-Silver, as shown inFIG. 2C.

Next, an inner rod or tube 20, here a rod, is positioned within the pairof semi-circular holes 25 of the TPG member 14 a, 14 b along thelongitudinal axis Z, as shown in FIG. 2C; the longitudinal axis Z beingparallel to the a-axis shown in 3F. The inner tube or rod 20 may besolid or hollow, metal or ceramic, for example, BeO, or it may be aninert glass ceramic that needs heat removed. It is noted that while herethe inner tube or rod 20 is shown having the same circular cross sectionof tube 10, the cross section of the inner tube rod 20 may be differentfrom that of the tube 10 and may have an oval cross section, a squarecross section, rectangular cross section, or any regular or irregularpolygon cross section or a cross section along any preferably,continuous closed loop.

Next, the upper and lower strictures 29 a, 29 b are brazed together withthe inner rod or tube 20 positioned centrally between the upper andlower strictures 29 a, 29 b within the bonded structure to produce thecompleted anisotropic thermal conduit 24 shown in FIG. 2D. It should benoted that the reactive metal braze alloy may be done sequentially aftereach application of braze or may be combined into fewer braze steps. Forexample, the outer tube 10 may be brazed on for each half 10 a, 10 b andthen another braze to attach the inner tube or rod 20 and combine thehalves 10 a, 10 b or the entire brazing may be done in one brazeoperation.

Referring now to FIGS. 4A and 4B, an exemplary pair of many, manyapplications for the anisotropic thermal conduit 24 is shown. Here, anarray of the anisotropic thermal conduits 24 is used as a heat spreaderto convey heat from a heat source 33 to a heat sink 34. FIG. 4A showsthe conduits 24 between the heat source 33 and the heat sink 34 withtheir longitudinal axis perpendicular to the surfaces of the heat source33 and the heat sink 34 and FIG. 4B shows the conduits 24 between theheat source 33 and the heat sink 34 with their longitudinal axisparallel to the surfaces of the heat source 33 and the heat sink 34. Itshould be understood that the conduit may be oriented relative to theheat source and heat sink in different configurations than that shown inFIGS. 4A and 4B.

Referring now to FIGS. 5A-5F, another embodiment of forming ananisotropic thermal conduit, here anisotropic thermal conduit 24′, isshown. Here, a thin, flexible sheet 40 of the TPG material, here havinga thickness of, for example, 0.015 inches is provided, as shown in FIG.5A. The upper and lower surface 42 a, 42 b, respectively, is in thebasal plane, (the a-axis, b-axis plane) as indicated again by the dottedline 15. A layer of a reactive metal braze alloy 43 a is deposited onthe outer walls of the inner tube or rod 20, as shown in FIG. 5B. Thethin, flexible sheet 40 of the TPG material is wrapped around the layerof the reactive metal braze alloy 43 a as shown in FIG. 5B. A secondlayer of the reactive metal braze alloy 43 b is deposited on the outerwalls of the TPG layer 40, as shown in FIG. 5C. The process repeats witha second layer of the thin, flexible sheet 40, here indicated as 40 a,of the TPG material wrapped around the second reactive metal braze alloy43 b. The process repeats until a structure 45 having predeterminedthickness of TPG material is produced. A reactive braze metal alloy 12a, 12 b such as described above in connection with FIG. 2C, is placed oneach one of two halves 10 a, 10 b, here half 10 a, of the cylindricaltube 10 (FIG. 2A) as shown in FIG. 5D. Next, the structure 45 havingpredetermined thickness of TPG material, is placed on the metal brazealloy 12 a, as shown in FIG. 5D. Next, a reactive metal braze metalalloy 32, such as described above in connection with FIG. 2C, is placedon one of two halves 10 a, 10 b, here half 10 a, of the cylindrical tube10 (FIG. 2A), and the other half 10 b is placed over the structure 45having predetermined thickness of TPG material to form the assemblyshown in FIGS. 5E and 5F. Next, the assembly is processed, as describedabove in connection with FIGS. 2C and 2D by brazing, to form thethermally anisotropic conduit 24′ as shown in FIGS. 5E and 5F. It isnoted that the anisotropic thermal conduit 24′ has concentric basalplanes, represented by the doted lines 15, disposed in concentriccircles, circumferentially about the longitudinal, Z-axis, or TPGa-axis, of the conduit 24′.

Referring now to FIGS. 6A-6I, another embodiment is shown for producingan anisotropic thermal conduit 24″. Thus, referring to FIG. 6A, a blockof TPG material 17 is provided. Next, a hole 60 is machined along thespatial Z-axis, corresponding to the c-axis of the TPG material(perpendicular to the upper and lower surface of the block 17; that is,perpendicular to the basal plane (which is in the spatial X-Y planecorresponding to the plane of the TPG material having the a-axis and theb-axis) represented by dotted line 15, to produce the structure 62 shownin FIG. 6B. Next, the structure 62 shown in FIG. 6B has its outersurface machined to form a rounded, donut shaped structure 64, as shownin FIGS. 6C and 6D. Next, the structure 64 is cut in half to produce anupper section 64 a and a lower section 64 b, as shown in FIG. 6E.Reactive braze material 16 is applied to inner tube or rod 20 and thenplaced in hole 60 formed between the upper and lower sections to providea structure 66 (FIG. 6F). A reactive metal braze alloy 12 b, such asdescribed above in connection with FIG. 2C, is placed on one of twohalves 10 a, 10 b, here half 10 b, of the cylindrical tube 10 (FIG. 2A)as shown in FIG. 6G. Next, the structure 66 having the inner tube or rod20 and the donut shaped TPG, is placed on the reactive braze metal alloy12 b, as shown in FIG. 6G. Next, a reactive metal braze alloy 12 a, suchas described above in connection with FIG. 2C, is placed on the otherone of two halves 10 a, 10 b, here half 10 a, of the cylindrical tube 10(FIG. 2A). The other half 10 a is placed over the structure 66 having areactive metal braze alloy coated, donut shaped TPG, to form theassembly shown in FIGS. 6H and 6I. Next, the assembly shown in FIG. 6His processed, as described above in connection with FIGS. 2C and 2D bybrazing, to form the thermally anisotropic conduit 24″. It is noted thatthe anisotropic thermal conduit 66 has basal planes, perpendicular tothe longitudinal, Z-axis of the conduit 24″.

Referring now to FIGS. 7A-7D, a plurality of the anisotropic thermallyconductive sheets 40, here for example TPG material as described abovein connection with FIG. 5A, are arranged edgewise in a regularly spaced,truncated semi-circular arrangement as shown and are bonded togetherwith reactive metal braze alloy 12 a to provide a structure 70 a. Thebasal plane 15 of the plurality of sheets 40 thus extend radiallyoutward from the spatial Z-axis, as indicated. The, a-Axis, b-Axis andthe c-Axis for an exemplary one of the sheets 40 is shown; the a-Axisbeing into the plane of the paper. The inner edges 73 of the sheets 40form a semi-circular region 72 a, as shown.

Referring now to FIG. 7B, a second structure 70 b like structure 70 a isformed; likewise forming a semi-circular region 72 b. The inner tube orrod 20 is aligned with a hole formed by the semi-circular regions 72 a,72 b, as shown and the aligned inner tube or rod 20, and structure 70 a,70 b are bonded together and to the inner tube or rod 20 with a reactivemetal braze alloy 32 as shown in a manner to form structure 74, as shownin FIG. 7D.

Referring now to FIG. 7C, the formed structure 74 is bonded to the innerwalls 11 a, 11 b of tube sections 10 a, 10 b, respectively (FIG. 2B) ina manner described in connection with FIGS. 5D and 5E to produce theanisotropic thermal conduit 24′″, shown in FIG. 7D. Here, the thermalconductivity of the anisotropic thermal material conducts heat radiallyoutwardly from the longitudinal axis of the tube.

Thermal conductivity, measured in watts per meter degree kelvin (W/m-°K) of the four thermal anisotropic conduits 24, 24′, 24″ and 24′″ werecalculated with results provided in the TABLE below. It should beunderstood that the X-axis, Y-axis, and Z-axis are mutuallyperpendicular axis and are referenced to the tube 10, the Z-axis beingaligned with the longitudinal axis, Z of the tube; whereas the a-AXIS,b-AXIS and c-axis are referenced to the anisotropic material 17 asdescribed above in connection with FIG. 3A. A model used for the thermalconductivity calculation is shown in FIG. 8 exemplifies the fourconfigurations (i.e., tubes 24, 24′, 24″ and 24′″). It was assumed thatthe inner tube or rod 20 was here a tube 20′ and that: it and the outertube 10 were made of copper; the inner diameter of the tube 20′ was 5mm, as shown; the outer diameter of the outer tube 10 was 10 mm, thethickness of each of the inner and outer tube 10, 20′ was 0.5 mm, andthe radial thickness of the TPG layer 17 used in the entire completedtube, (24, 24′, 24″ or 24′″) was 1.5 mm, as shown in the diagram, inFIG. 8. The thermal conductivity of the copper of the inner tube 20′ andthe outer tube 10 was 400 W/m-° K. The thermal conductivity of the TPGwas 1500 W/m-° K in basal plane and 10 W/m-° K perpendicular to thebasal plane. Calculated thermal conductivity values neglect the thinreactive metal braze alloy layers.

TABLE THERMAL THERMAL THERMAL THERMAL Thermal ANISOTROPIC ANISOTROPICANISOTROPIC ANISOTROPIC Conductivity, K CONDUIT 24 CONDUIT 24^(′)CONDUIT 24″ CONDUIT 24″′ Kx (W/m-° K) 714 16 714 714 (from the outeredge of tube 10 the inner edge of tube 20′ along the X-axis. FIG. 8.) Ky(W/m-° K)  16 16 714 714 (from the outer edge of tube 10 to the inneredge of tube 20′ along the Y-axis. FIG. 8.) Kz (W/m-° K) 1060  1060  1661060  (from a front flat face of the conduit 24 (a face of the conduit24 in the X-Y plane) to an opposite flat face of the conduit 24 (a faceof the conduit 24 in the X-Y plane) along the length of conduit 24; thatis along the Z-axis. FIG. 8.) THERMAL Along the Along the Along theAlong the CONDUCTION X-axis and Z-axis X-axis and X-axis, the DIRECTIONthe Z-axis the Y-axis Y-axis, and (The basal the Z-axis plane of the(radially TPG is in the outward from X-Z plane the longitudinal of thetube 20) axis, Z) THERMAL Along the Along the Along the NOT INSULATIONY-axis X-axis and Z-axis APPLICABLE DIRECTION the Y-axis

By creation of the anisotropic thermal tubular conduit 24 (FIG. 2D),performance can be enhanced due to the opportunity to reduce the numberof transitions from the heat source to the heat sink (FIG. 4). Due tothe anisotropic nature of the TPG, the heat flow can be controlled inmultiple ways as shown in the examples above. The heat may be directedradially along the plane perpendicular to the longitudinal axis Z-axis)as in conduit 24″ and 24′″ or primarily along the plane parallel to theZ axis, as in conduit 24 and 24′ providing design flexibility andopportunity for additional system benefits.

A number of embodiments of the disclosure have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the disclosure. Forexample, with rod 20 a hollow tube, a coolant may be passed through sucha hollow tube. Further, while here the tube 10 and the rod 20 have acommon central axis, here designated as the Z-axis, the central axis ofthe rod 20 may be laterally offset from the central axis of the tube 20.Still further, the material used to form the various embodiments of theconduit may be flexible to provide bendable conduits. Also, the tube 10may have a curved longitudinal axis, Z. Additionally it should be notedthat reactive metals such as titanium or vanadium may be mixed in asreactive braze filler or deposited on the surfaces to be braze.Alternate bonding materials may be used. Accordingly, other embodimentsare within the scope of the following claims.

What is claimed is:
 1. An anisotropic thermal conduit comprising: an outer structure; and an anisotropic thermal material disposed within, and thermally coupled to, the outer structure.
 2. The anisotropic thermal conduit of claim 1 wherein the anisotropic thermal material has a greater thermal conductivity along a longitudinal axis of the outer structure than the thermal conductivity of the anisotropic thermal material along a direction perpendicular to the longitudinal axis of the outer structure.
 3. The anisotropic thermal conduit of claim 1 wherein the anisotropic thermal material has a smaller thermal conductivity along a longitudinal axis of the outer structure than the thermal conductivity of the anisotropic thermal material along a direction perpendicular to the longitudinal axis of the outer structure.
 4. The anisotropic thermal conduit of claim 1 wherein the anisotropic thermal material has a smaller thermal conductivity along a direction circumferentially within the outer structure than the thermal conductivity of the anisotropic thermal material along a direction along the longitudinal axis of the outer structure.
 5. The anisotropic thermal conduit of claim 1 wherein the anisotropic thermal material is embedded with the outer structure.
 6. The anisotropic thermal conduit of claim 1 wherein the outer structure is a thermally conductive metal.
 7. The anisotropic thermal conduit of claim 1 including an inner or rod and wherein the anisotropic thermal material is disposed between the inner or rod and the outer structure.
 8. The anisotropic thermal conduit of claim 1 wherein the outer structure has a circular cross-section.
 9. The anisotropic thermal conduit of claim 1 wherein the inner rod or has a circular cross-section.
 10. The anisotropic thermal conduit of claim 1 wherein the outer is a metal.
 11. The anisotropic thermal conduit of claim 1 wherein the outer is MoCu, WCu. W, Mo, Cu,
 12. The anisotropic thermal conduit of claim 1 wherein the inner or rod is a metal, a ceramic, glass or a plastic.
 13. The anisotropic thermal conduit recited in claim 1 wherein the thermal conductivity of the anisotropic thermal material conducts heat radially outwardly from the longitudinal axis of the.
 14. The anisotropic thermal conduit recited in claim 1 wherein the anisotropic thermal material has a basal plane perpendicular to the longitudinal axis of the outer structure.
 15. The anisotropic thermal conduit recited in claim 1 wherein the anisotropic thermal material has a basal plane parallel of a longitudinal axis of the outer structure.
 16. The anisotropic thermal conduit recited in claim 1 wherein the anisotropic thermal material has a basal plane perpendicular extending radially outwardly from a longitudinal axis of the outer structure.
 17. The heat transfer system recited in claim 1 wherein the anisotropic thermal material has a basal plane, an outer edge of the basal plane being in contact with the outer structure.
 18. The heat transfer system recited in claim 1 wherein the anisotropic thermal material has a basal plane extending radially outward from an inner region of the outer structure.
 19. The heat transfer system recited in claim 1 wherein the anisotropic thermal material comprises a plurality of sheets of anisotropic thermal material, edges of the sheets extending radially outwardly from an inner region of the outer structure, outer edge of the sheets being thermally coupled to the outer structure, a surface of one of the sheets being thermally coupled a surface of an adjacent one of the sheets.
 20. The heat transfer system recited in claim 1 wherein the anisotropic thermal material has a basal plane perpendicular to a longitudinal axis of the outer structure.
 21. The heat transfer system recited in claim 1 wherein the anisotropic thermal material comprises a plurality of sheets of anisotropic thermal material, each one of the a plurality of sheets having a basal plane therein, the basal plane of each one of the sheets being disposed around a longitudinal axis of the outer structure, the plurality of sheets being disposed successively outwardly from the longitudinal axis of the outer structure, the sheets being thermally coupled one to another, an outer one of the sheets being thermally coupled to the outer structure.
 22. The heat transfer system recited in claim 1 wherein the anisotropic thermal material has a basal plane parallel to a longitudinal axis of the outer structure.
 23. A heat transfer system, comprising: a heat source; a heat sink; an anisotropic thermal conduit interposed between the heat source and the heat sink to transfer heat from the heat source to the heat sink, the anisotropic thermal conduit comprising: an outer structure; and an anisotropic thermal material having a basal plane, the anisotropic thermal material being disposed within, and thermally coupled to, the outer structure; wherein the heat source and the heat sink are disposed externally of, and thermally coupled to, the outer structure; and wherein one portion of the basal plane is thermally coupled to the heat source and another portion of the basal plane is thermally coupled to the heat sink to conduct heat from the heat source to the heat sink through the basal plane.
 24. The heat transfer system recited in claim 23 wherein the basal plane is in direct contact with the heat source and the heat sink.
 25. A method for transferring heat from a heat source to a heat sink, comprising: providing a anisotropic thermal conduit comprising: an outer structure; and an anisotropic thermal material disposed with, and thermally coupled to, the outer structure, the heat source and the heat sunk being disposed externally of, and thermally coupled to, the outer structure, the anisotropic thermal material having an opening passing therethrough; and passing a coolant through the opening. 